The present invention relates to exhaust means and more particularly to muffled exhaust means for outboard marine engines.
Conventionally, outboard marine engines have exhaust passages which normally open into water so that engine exhaust gas is expelled into water. Further, in order to make exhausting of combustion gas possible under an idling or low speed engine operation wherein the exhaust gas pressure is insufficient to expel the exhaust gas into water, the outboard marine engines are additionally provided with auxiliary exhaust ports which open into air. Where the outboard marine engines are designed for use in lakes, ponds or the like, it may not be allowed to exhaust the engine combustion gas into water in order to avoid possible pollution of water by the engine exhaust gas.
Thus, outboard marine engines are always provided with exhaust passages which open into air so that they must also provided with means for attenuating exhaust noise. For the purpose, conventional outboard marine engines include a housing having an expansion chamber into which the engine exhaust pipe is projected. The housing is also formed with a radial partition wall which projects inwardly into the expansion chamber and encircle the exhaust pipe with a small clearance so as to divide the expansion chamber into two compartments which are connected together through a restricted flow passage defined by the clearance between the partition wall and the exhaust pipe. Thus, there is provided an exhaust passage wherein the exhaust gas from the exhaust pipe is first subjected to an expansion at the first expansion compartment, then forced to pass through the restricted flow passage and thereafter again allowed to expand at the second expansion compartment before it is exhausted.
In this known type of engine exhaust system, inconveniencies have been experienced in that the location of the partition wall cannot be arbitrarily determined owing to the configuration and manner of manufacture of the housing. In general, such a housing of an outboard marine engine has an appearance wherein the widthwise dimension is gradually decreased from the top and bottom ends toward the intermediate portion thereof with the smallest width at the intermediate portion. Since such a housing is usually formed by means of a casting technique, it has been very difficult to locate the aforementioned partition wall other than the portion where the widthwise dimension of the housing is the smallest because removal of casting cores may become very difficult. Further, due to the similar reasons, it has been very difficult to provide two or more axially spaced partition walls in the housing for the purpose of increasing the number of expansion compartments.
It is therefore an object of the present invention to provide exhaust means for an outboard marine engine wherein the aforementioned problems can be overcome.
Another object of the present invention is to provide exhaust means for an outboard marine engine which is easy to manufacture but provides for versatility of design.
A further object of the present invention is to provide novel exhaust means for an outboard marine engine which includes a plurality of expansion compartments for attenuating exhaust noise.